1. Field of the Invention
The present invention relates to a scroll type fluid machine used, for example, as a component in a refrigeration cycle, etc.
2. Description of the Prior Art
Recently, for air conditioning units, scroll type compressors (or scroll type fluid machines) in which a pair of mutually engaged spiral wraps are provided have been used because of their high efficiency operation.
In FIG. 4, an example of a heretofore known scroll type compressor is shown, and this scroll type compressor is now described. In FIG. 4, numeral 1 designates a hermetic housing. This hermetic housing 1 consists of a cup-like body 2, a front end plate 4 fixed thereto by bolts 3 and a cylindrical element 6 fixed thereto by bolts 5. A rotating shaft 7, passing through the cylindrical element 6, is supported rotatably by the housing 1 via a bearing 8 and a bearing 9.
Within the hermetic housing 1, a stationary scroll 10 (one of the pair of scroll elements) and a swivel scroll 14 engaged therewith (the other of the pair of scroll elements) are provided.
More particularly, the stationary scroll 10 has an end plate 11 and a spiral wrap 12 standing on its inner surface. The end plate 11 is fixed to the bottom side of the cup-like body 2 by bolts 13.
The outer circumferential surface of the end plate 11 and the inner circumferential surface of the cup-like body 2 sealingly contact each other, and thereby the inner space of the housing 1 is partitioned so that, in a space within the hermetic housing 1, a discharge cavity 31 is formed on the other side of the end plate 11 and a suction chamber 28 is formed on the inner side of the end plate 11.
Incidentally, at the central part of the end plate 11, a discharge port 29 is provided so as to be opened and closed by a discharge valve 30.
The swivel scroll 14 has an end plate 15 and a spiral wrap 16 standing on its inner surface. The spiral wrap 16 is of substantially the same shape as the spiral wrap 12 of the stationary scroll 10.
The swivel scroll 14 and the stationary scroll 10 are mutually engaged eccentrically by a length of a radius of revolution with a deviation angle of 180 degrees, as shown in the figure. On a tip surface of each spiral wrap 12, 16, a spiral tip seal 17, 18 is provided ridgedly along the spiral.
As to the fitting of the tip seal 17, a groove 17a is formed along the spiral on the tip surface of the spiral wrap 12, and the spiral tip seal 17 is inserted in the groove 17a so that a portion of one side of the tip seal 17 is projecting from the tip surface of the spiral wrap 12. Likewise as to the fitting of the tip seal 18, a groove 18a is formed along the spiral on the tip surface of the spiral wrap 16 and the spiral tip seal 18 is inserted in the groove 18a so that a portion of one side of the tip seal 18 is projecting from the tip surface of the spiral wrap 16.
The tip seal 17 os the spiral wrap 12 sealingly contact the inner surface of the end plate 15 of the opposite swivel scroll 14, and the tip seal 18 of the spiral wrap 16 sealingly contacts the inner surface of the end plate 11 of the opposite stationary scroll 10.
The side surfaces of the spiral wrap 12 and the spiral wrap 16 make line contacts at a plurality of places and thereby form a plurality of crescent compression chambers 19a, 19b (fluid chambers) at the positions between the wraps which have nearly a point symmetry with each other around the centers of the spirals.
Within a cylindrical boss 20 projecting at the central part of the outer surface of the end plate 15, a drive bush 21 is inserted rotatably via a rotary bearing 23. Within a slide groove 24 provided in the drive bush 21, an eccentric drive pin 25 is provided eccentrically to project at the inner end of the rotating shaft 7, and is inserted slidably. The drive bush 21 is fitted with a balance weight 27 for balancing dynamic unbalances caused by orbital swivel motions of the swivel scroll 14.
Incidentally, in FIG. 4, numeral 36 designates a thrust bearing provided between the circumferential edge of the outer surface of the end plate 15 and the inner surface of the front end plate 4, numeral 26 designates a rotation preventing mechanism consisting of an Oldham coupling for allowing orbital swivel motions of the swivel scroll 14 but preventing rotation thereof, and numeral 37 designates a balance weight fixed to the rotating shaft 7.
In a scroll type compressor so constructed, upon the rotating shaft 7 being driven, the swivel scroll 14 is driven via an orbital drive mechanism consisting of the eccentric drive pin 25, the drive bush 21, the cylindrical boss 20, etc.
Then the swivel scroll 14, being prevented from rotating by the rotation preventing mechanism 26, makes orbital swivel motions on a circular track having a radius of revolution, i.e. a radius which is an eccentric amount between the rotating shaft 7 and the eccentric drive pin 25.
Then, the line contact parts of the side surfaces of the spiral wrap 12 and of the spiral wrap 16 move gradually in the direction of the spiral centers. As a result, the compression chambers 19a, 19b move, with the volume thereof being reduced, in the direction of the spiral centers.
Accompanying such movement of the compression chambers 19a, 19b, a gas (fluid) flows into a suction chamber 28 through a suction inlet (not shown in the figure) and is taken into each of the compression chambers 19a, 19b from openings of the outer ends of the spiral wraps 12, 16 and, while being compressed, comes into the central chamber 22. Upon completion of compression, it passes through the discharge port 29 by pushing open the discharge valve 30, and the gas is discharged into the discharge cavity 31 and flows out through a discharge outlet (not shown in the figure).
Incidentally, the movement occurring at the swivel scroll 14 while it is making orbital swivel motions is allowed by the slide groove 24. I.e. while the swivel scroll 14 is making orbital swivel motions, it receives a centrifugal force acting in the direction of eccentricity and a gas pressure by the compressed gas in each of the compression chambers 19a, 19b and is pushed in the direction increasing the orbital radius.
With such motions, the side surfaces of the spiral wrap 16 of the swivel scroll 14 sealingly contact the side surfaces of the spiral wrap 12 of the stationary scroll 10, by which leakage of the gas from the compression chambers 19a, 19b is prevented. The motions of the swivel scroll 14 of which the orbital radius is about to change when the side surface of the spiral wrap 12 and the side surface of the spital wrap 16 are making sliding motions in each other while they are maintaining sealing contact are allowed by the eccentric drive pin 25, which makes sliding movements within the slide groove 24 in its longitudinal direction.
In a scroll type compressor, a weight reduction of both the stationary scroll 10 and the swivel scroll 14 is being pursued. For this purpose, in the prior art, the stationary scroll 10 and the swivel scroll 14 are mode of an aluminum material. The spiral wraps 12, 16 of both scrolls 10, 14 are also made of an aluminum material and the tip seals 17, 18 are made of a composite plastic material, as has so far been used, composed of a polyphenylene sulfide (PPS) as a base material and a carbon filter of 15 weight percent and others as a filler, and are used in combination.
However, the stationary scroll 10 and the swivel scroll 14 made of an aluminum material, if used, have the disadvantage that extreme wear occurs or a seizure can occur, etc.
Therefore, one of the scrolls has a hard surface treatment applied thereto. More concretely as shown in FIG. 5, one of the scrolls, for example, the movable swivel scroll 14, has a surface treatment applied on its surface such as an alumite (aluminum is anodized and an aluminum oxide coating is formed on the surface), a special alumite (aluminum is anodized, aluminum oxide coating is formed on the surface and a fluororesin etc. is impregnated on the surface), etc.
However, while a hard aluminum oxide coating is formed by this surface treatment on the inner surface of the end plate 15 of the swivel scroll 14, the surface roughness becomes worse than that of the aluminum material.
For this reason, upon the swivel scroll 14 being driven, the tip seal 17 of the stationary scroll 10 making sealing contact with the inner surface (the surface being made hard and the surface roughness being worsened by a surface treatment) of the end plate 15 of the swivel scroll 14, and the tip seal 18 of the swivel scroll 14 making sealing contact with the inner surface (soft surface of aluminum material itself) of the end plate 11 of the stationary scroll 10, make relative sliding motions between their respective components, and sliding wear occurs between the relative surfaces.
More concretely, at the portion where the top seal 17 of the stationary scroll 10, made of a composite plastic material (composed of a polyphenylene sulfide as a base material and a carbon fiber of 15 weight percent and others as a filler) and the end plate 15 of the swivel scroll 14 having a surface treatment make sealing contact (combination of a composite plastics and a treated surface), there occurs a considerable sliding wear on the side of the tip seal 17. Likewise at the portion where the tip seal 18 of the swivel scroll 14 and the end plate 11 of the stationary scroll 10 made of an aluminum material make sealing contact (a combination of a composite plastic and an aluminum material), there occurs a considerable wear on the side of the end plate 11. And yet gradually, a sliding wear grows quickly as the contact pressure becomes larger.
Therefore, if a compressor is operated in a state referred to as a high differential pressure operation, where the differential pressure of the discharge pressure and the suction pressure is large, as the contact pressure between the tips of tip seals 17, 18 and the inner surfaces of the end plates 11, 15 becomes larger, the wear of one component grows quickly. I.e. the wear of the tip seal 17 of the stationary scroll 10 and the wear of the inner surface of the end plate 11 of the stationary scroll 10 increases more quickly than that of the engaging swivel scroll 14, which leads to a problem in that the life of the product is hurt.